Such heating systems are used in vehicles in order to bring the interior space of a vehicle to desired temperatures in a parking heating mode or also in an auxiliary heating mode. The temperature to which the interior space of the vehicle is to be preheated may be preset, for example, by a user of the vehicle, so that, on the one hand, comfortable temperatures will prevail in the interior space of the vehicle at the beginning of the travel, e.g., in the winter, and, on the other hand, the windshields are already defogged and the greatest possible safety is offered.